Internet sockets

In RFC documents relating to TCP or UDP, a socket on a certain host is defined as the combination of an IP address and a port number.

The BSD operating system introduced network sockets in 1983: see the Berkeley sockets API. Each socket gets bound to a given port, which lets the transport layer protocol (typically UDP or TCP) identify which application to send the data to.

Unix domain sockets, IPC sockets

Another type of socket is used by POSIX compliant systems, and are called Unix domain sockets. Their primary function is as a means for inter-process communication and are therefore also called IPC sockets. These connections are from the local computer to itself, not actually a connection transmitted over a physical network.